Chris Hartjes, a big proponent of testing in the PHP community, has a new post to his blog about a new testing tool he's released to make it easier for you to know what needs testing - Tricorder.

I've hacked together a little CLI script that I think will be of use to many people who are trying to answer the question "just what should I do to test this thing anyway?" as they learn how to write PHPUnit tests to go along with their code. [...] I've created something that I am calling PHP-Tricorder, a CLI utility that can be used in conjunction with phpdoc structure.xml files to make suggestions on testing scenarios. It's at a 0.1 release right now, so I anticipate it will grow and add more features as time goes on.

The post includes an example of the output generated from the phpdoc's XML output, recommending things like:

Mocking certain objects

Testing for data types and contents

Recommending testing ideas for private/protected methods

You can grab (or contribute to!) the latest version of the tool over on github.